Traveling Wave Reactors

Ahmed Sharif
March 21, 2011

History and Current Status

The concept of the traveling wave reactor (TWR) was
first proposed in 1958 at a International Atomic Energy meeting. [1] The concept
essentially involved the idea that a reactor could be designed to create and consume (i.e.
"breed-and-burn) its own fuel, given raw material. This "breed-and-burn"
reactor concept caught the attention of Dr. Edward Teller; however, the concept remained
largely ignored by the rest of the scientific community until recent years. [1]

In the past few years, TWR technology has gained the interest of not only the scientific
community, but also the private sector. Leading the forefront of TWR research and development
is Dr. Lowell Wood and his collaborators at Terrapower, a privately funded research company
based in the U.S. [2] While currently TWRs exist only virtually, in Terrapower software,
the concept is far enough along in development where a test version of the reactor could be built;
Terrapower is in the process of seeking a customer and a host country
for such a purpose. [2]

How it Works

Unlike conventional reactors which use uranium-235
for fuel, TWRs largely rely on uranium-238, a byproduct of conventional
nuclear reactors, for fuel (roughly 90 percent of fuel requirements) and
only marginally rely on enriched uranium. [1,3] To utilize uranium-238,
TWRs initially require a fission reaction involving the enriched
uranium. This reaction then sets off a chain reaction which breeds
fissible fuel, plutonium-239, from the remaining uranium-238. [1,3] The
plutonium-239 subsequently undergoes fission; this provides energy
output and the "breed-and-burn" cycle propagates through the life of the
reactor. [1,3] Given certain assumptions about size and amount of fuel
in a reactor, some scientists believe that TWRs may be able sustain
energy production for decades without requiring refueling. [1]

With respect to physical parameters, the core of
TerraPower's design is a cylinder, 10 feet wide and 13 feet long. [2]
Regarding power production capacity, an individual TWR unit is expected
provide about 500 MWe; this is in comparison to the
1,000 MWe plus designs of modern light-water reactors. [2]

Traveling Wave Reactor Advantages

TWR technology has several economic, environmental,
and political advantages when compared to other nuclear reactor
technologies. These advantages generally relate to the fueling
characteristics of TWRs; as noted above, TWRs meet the majority of their
fueling requirements with waste uranium and only marginally require
enriched uranium. [3] Additionally, TWRs may be able to run for decades
without refueling and fuel removal. [1] Because of these
characteristics, TWRs in theory would incur lower fueling costs than
conventional reactors. In addition to these economic advantages, the
fueling characteristics of TWRs provide benefits related to
environmental preservation and national security as well. TWRs can, to
a significant extent, "recycle" waste uranium byproducts derived from
the operation of conventional nuclear reactors; if TWRs were widely
deployed and substituted for new light-water reactor constructions,
there would be a reduced need for uranium mining, uranium enrichment,
spent nuclear fuel reprocessing, and nuclear waste disposal. In theory,
a reduced need for these processes would translate to reduction of
society's impact on the environment, holding all other assumptions
constant. Moreover, because uranium enrichment and spent fuel
reprocessing are two significant sources of nuclear proliferation risk,
a reduced need for these services and associated facilities would
translate to a reduction in nuclear proliferation risk. [4]

Traveling Wave Reactor Uncertainties and Risks

Because no TWR facilities have yet been built, the
actual economics of these reactors have yet to be realized.
Additionally, the U.S. does not yet have a certification process for
TWRs; as such, it may be a decade or more before a TWR test reactor
could be built in the U.S. [2] With respect to safety concerns, like
other breeder reactor designs, TWRs use liquid sodium as coolant; liquid
sodium reacts strongly with air and water and thus poses a significant
hazard. [1,3]